Biomedical subjects
G Syme
Publications and source records attributed to G Syme.
Effect of diet upon enterocyte differentiation in the rat jejunum.
Positional and temporal correlates for the development of microvillus membranes and for two of the hydrolytic enzymes they contain have been determined and compared with the ability of enterocytes to transport valine during migration from crypt base to villus tip in jejunal tissue taken from rats maintained on diets containing different amounts of protein. Microvillus elongation and the appearance of both aminopeptidase N (APN) and isomaltase (IM) activities reached maximal rates of expression in enterocytes located 16 +/- 5 micron from the crypt-villus junction. This close positional correlation was not found for the later development of the valine transport function. Feeding rats isoenergetic diets containing 20% instead of 5% protein caused significant increases in both villus height and crypt depth without changing the positional correlations described above. The maximal rates for microvillus elongation and APN and IM appearance were greater and occurred earlier in enterocytes taken from rats fed a high-protein diet. The time of onset and capacity to transport valine were found to be closely correlated for rats maintained on high- and low-protein diets. The ratio of APN to IM activity in fully differentiated enterocytes was either 0.7 or 1.2 depending on whether rats had been fed a low- or high-protein diet. The maximal length of microvillus membranes in fully differentiated enterocytes from rats on a low-protein diet was 1.4 times that found in rats maintained on a high-protein diet. Possible ways in which the microvillus membrane structure of enterocytes, enzyme activity and the ability to transport amino acids might be controlled are discussed. Relative estimates are also made of the probable effects that changes in diet will have on the capacity of the intestine to digest and absorb nutrients.
Cell differentiation and L-ornithine decarboxylase activity in the small intestine of rats fed low and high protein diets.
L-Ornithine decarboxylase activity is higher in enterocytes from rats fed low protein rather than high protein diets. Intestinal cell proliferation rate is 50% higher in rats fed high protein than low protein diets. This is not consistent with a direct role of ornithine decarboxylase in intestinal proliferation. It is shown that ornithine decarboxylase is preferentially associated with differentiating villus cells in intestine from rats fed low protein diets.
Intestinal adaptation of protein deficiency.
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The effect of protein-deficient isoenergetic diets on the growth of rat jejunal mucosa.
1. Newly weaned 21-d-old male rats were given isoenergetic diets containing 200, 100 and 50 g protein/kg for 7, 14, 28 or 70 d. The mid-jejunum was removed from the rats and a micrometric analysis of the mucosa was made. The following measurements were made: number of villi/mm2, villus dimensions, villus surface area, crypt depth, crypt: villus, the number of cells/crypt in metaphase arrest per h. 2. Comparison were made between animals of the same age but on different diets, and animals on the same diet but of different ages. The latter comparison gave information on the effect of protein deficiency on the pattern of maturation of each feature of the villus or crypt studied. 3. The effect of protein deficiency was not consistent at each stage of maturation. For instance villus height was decreased when compared with the controls following 28 d on a protein-deficient diet but not after 7 or 70 d. 4. The only measurement to be unaffected by protein deficiency was the number of villi per unit area. 5. In general the 50 g protein/kg diet had a more pronounced effect than the 100 g protein/kg diet. Protein deficiency delayed maturation by either slowing or inhibiting changes seen in normal maturation. 6. In rats given 50 g protein/kg diet, although the villus surface area did not increase as the rats matured there were increases in epithelial cell production rate and number of crypts per villus.
Functional differentiation of enterocytes in the follicle-associated epithelium of rat Peyer's patch.
The ability of the follicle-associated epithelium (FAE) of rat Peyer's patch to accumulate valine has been measured using a new technique of autoradiographic analysis. Maximum uptake of valine was achieved by enterocytes present in the dome region of the FAE. Valine uptake was not seen in enterocytes present on the lower slopes of the FAE or in follicle-associated crypts. The ability of the FAE to absorb valine was generally much less than that seen in enterocytes present on adjacent villi. The main reason for this discrepancy lay in the apparent inability of the FAE to develop a second phase of amino acid transport similar to that seen in villus enterocytes. It is suggested that this failure results from some unexplained interaction taking place between the FAE and its underlying lymphoid tissue.
The validity of assessing changes in intestinal absorption mechanisms for dietary sugars with non-metabolizable analogues (glucalogues).
1. Transfer potentials were obtained from everted jejunal sacs prepared from fed euthyroid, fasted euthyroid, fed hypothyroid and fasted hypothyroid rats by addition of serial concentrations of the dietary sugars glucose and galactose and the glucalogues 3-0-methyl glucose, alpha-methyl glucoside and 6-deoxy-D-glucose to the incubation fluids. The kinetic parameters of 'apparent Michaelis constant' (apparent Km) and maximum transfer potential difference (pdmax) obtained from the results were used to characterize the changes in the electrogenic transfer mechanisms for these substrates. 2. Analysis of the significant differential changes in values for 'apparent Km' and pdmax for the two dietary sugars and the three glucalogues indicated heterogeneity in the mechanisms for sugar transfer across the intestine and suggested a minimum of four possible carriers. 3. The validity of using glucalogues to characterize changes in the transfer mechanisms for the dietary sugars in different dietary and hormonal states was assessed. None of the kinetic parameters for electrogenic glucalogue transfer matched those for the dietary sugars in all the experimental conditions. The employment of glucalogues to assess changes in electrogenic transfer mechanisms for dietary sugars can thus lead to invalid conclusions. 4. Fasting decreased the 'apparent Km' of dietary sugars and the glucalogues. However, the pdmax values for glucose, galactose, and alpha-methyl glucoside decreased whereas those for 3-0-methyl glucose and 6-deoxy-D-glucose did not. 5. Hypothyroidism showed different effects in fed and fasted intestine. Because hypothyroidism induced a reduction in food intake, separation of the direct effects of the condition on electrogenic transfer from reduced food intake effect was not possible.
The effect of low protein diets on the small intestinal mucosa of the rat [proceedings].
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The effects of hypothyroidism and fasting on electrogenic amino acid transfer: possible evidence for multiple neutral amino acid carrier systems in rat jejunum.
The jejunal mechanisms for the electrogenic transfer of four neutral amino acids (alanine, leucine, methionine, valine) and for sarcosine were characterised by an electrical method in vitro. The values for apparent Km obtained electrically agree well with those assessed by conventional chemical techniques. Hypothyroidism and/or fasting rats for 3 days induced differential changes in the apparent Km and p.d.max for the various amino acids. These alterations were interpreted as indicating the presence of at least three mechanisms for neutral amino acid transfer and one for sarcosine. In euthyroid rats, only alanine showed changes in apparent Km (decrease) and p.d.max (decrease) after fasting for 3 days. With hypothyroidism the kinetic parameters of electrogenic transfer for alanine, valine and sarcosine were significantly altered while those for leucine and methionine were unaffected.
Effect of altered thyroid status induced by thyroid hormones, goitrogens and diet on intestinal electrogenic valine transfer.
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Thyroid control of small intestinal oxygen consumption and the influence of sodium ions, oxyhen tension, glucose and anaesthesia.
1. Oxygen consumption of jejunum removed from either killed or anaesthetized euthytoid, hypothyroid and triiodothyronine (T3)-treated rats was measured polarographically in vitro. 2. Hypothyroidism induced by drinking 6-n-propyl-2-thiouracil depressed jejunal oxygen consumption. 3. Treatment of euthyroid rats with T3 stimulated jejunal oxygen consumption by 39% in the presence of 28 mM glucose and by 23% in its absence. 4. Sodium ions appear to play a major permissive role in the action of T3 on jejunal oxygen uptake. In the presence of sodium, T3 stimulated significantly the oxygen consumption by 23% while in the absence of sodium the stimulation was only 10% which was not significant. The sodium-sensitive oxygen uptake of the jejunum was expanded by 57% after T3 treatment.
The influence of oxygen tension, glucose and anaesthesia on the oxygen consumption of the jejunum from normal and hypothyroid rats.
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Changes in the performance of the electrogenic transfer mechanisms of the small intestine related to different sources of a commercial feeding diet for rats.
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Effectiveness of thyroxine and triiodothyronine in surgical and prophylthiouracil induced hypothyroidism assessed by changes in intestinal electrogenic transfer.
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Differential changes in the 'apparent Km' and maximum potential difference of the hexose and amino acid electrogenic transfer mechanisms of the small intestine, induced by fasting and hypothyroidism.
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Ultrastructure of small-intestinal epithelium in weaned and unweaned pigs and pigs with post-weaning diarrhoea.
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